This is an interesting question from a book I have been reading. It is exploring the notion of God defined as follows:
A person without a body (i.e. a spirit), present everywhere, the creator and sustainer of the universe, able to do everything (i.e. omnipotent), knowing all things (i.e. omniscient), perfectly good, a source of moral obligation, immutable, eternal, a necessary being, holy, and worthy of worship.
The question explored, as you might guess, is about being
perfectly good. The "problem of evil" existing in the world has been discussed here many times. Basically the question is , how can God be
perfectly good (or all loving) when he lets things happen like , for example, young children to be abducted, raped and murdered. The answer usually comes in something resembling this other quote from the book I spoke of, attributed to a Joseph Butler:
Upon supposition that God exercises a moral government over the world, the analogy of this natural government must be a scheme quite beyond our comprehension; and this affords a general answer to all objections against the justice and goodness of it.
In other words, "God works in mysterious ways". The morals and goodness of god are just simply beyond our comprehension. As the author points out, such an answer does 2 things. First it makes it indefeasible. I.e. it cannot be disproved. But, it also makes it insupportable. For, if the scheme is "beyond our comprehension", then we cannot look at individual occurrences in the real world and decide if they support such a Godly scheme or not.
In more plain language I would just say that it basically redefines the word "good" to be something unrecognizable by human beings. We have some concept of what the word good means but , since the events in the world do not always meet that definition, the theist who defines God as above has to redefine the word good to mean something else. Essentially the definition of good becomes: "the way the world actually is".
The author calls this problem of an indefeasible, insupportable perfectly good God the "Falsification Challenge" and states it as this:
Someone tells us that God loves us as a father loves his children. We are reassured. But then something awful happens. Some qualification is made... We are reassured again. But perhaps we ask: what is this assurance of God's (appropriately qualified) love worth, what is this apparent guarantee really a guarantee against? Just what would have to happen not merely to tempt but also (logically and rightly) to entitle us to say "God does not love us" or even "God does not exists"?